1. Field of the Invention
The present invention relates to a webbing retractor for winding up an occupant restraining webbing and, more particularly, to a webbing retractor for use in a seatbelt system for a vehicle which is so designed that it can selectively be set in two states, that is, one wherein, after an occupant restraining webbing has been fastened to the occupant's body, it is prevented from being unwound at all times, and the other wherein a webbing take-up shaft is locked from rotating in the direction in which the webbing is unwound only when an emergency situation of the vehicle occurs.
2. Description of the Related Art
A typical conventional webbing retractor which is installed on a vehicle incorporates a lock mechanism adapted to lock, when necessary, a webbing take-up shaft from rotating in the direction in which an occupant restraining webbing is unwound.
There are two types of lock mechanism: one which is known as "ELR" (Emergency Locking Retractor) wherein, when the vehicle is in a normal state, the webbing is allowed to be unwound and rewound as desired, whereas, when the vehicle runs into an emergency situation, this is sensed by an acceleration sensor and the take-up shaft is instantaneously locked from rotating in the direction in which the webbing is unwound; and the other which is known as "ALR" (Automatic Locking Retractor) wherein, after the webbing has been fastened to the occupant's body, the take-up shaft is locked from rotating in the direction in which the webbing is unwound.
In the ELR, when the vehicle is running in a normal state, the occupant who has the webbing fastened can freely wind the webbing in and out on the take-up shaft so as to assume a desired driving posture.
In the ALR, on the other hand, after a predetermined amount of webbing has been unwound, it is prevented from being unwound from the take-up shaft, which means that the occupant's body can reliably be restrained by the webbing.
One type of webbing retractor which is provided with both ELR and ALR systems has already been disclosed (see, for example, the specification of Japanese Utility Model Laid-Open No. 76252/1984).
This type of conventional retractor is so designed that the ELR and ALR modes can be switched over from one to the other according to need. More specifically, when the webbing is fully rewound on the take-up shaft, a pawl which is engageable with a lock wheel by means of a biasing force is forced to disengage from the lock wheel and prevented from reengaging with it, thereby bringing the retractor under the control of lock means activated by the acceleration sensor. When the webbing, after it has fully been unwound, is rewound, the pawl is enabled to engage with the lock wheel, so that it is possible to prevent the webbing from being unwound thereafter.
Accordingly, a single webbing retractor can selectively serve as ELR and ALR according to need.
The above-described conventional webbing retractor suffers, however, from the following problems.
Since the structure for effecting switching over between ELR and ALR is complicated and requires a relatively large number of parts, the assembling operation is complicated and troublesome, disadvantageously.
Further, when ALR is to be switched over to ELR, the webbing must be fully rewound, and during this rewinding operation, the lock wheel rotates together with the take-up shaft while being in contact with the pawl, resulting in generation of chattering noise.